First of all, remember that it lies indirectly. The US government doesn't ever knowingly make false statements. We don't accuse people of doing something that we did. Because that destroys our reputation and America values it's reputation more than you can imagine. Not just among other countries but among it's own citizens. We love to think of ourselves as the good guys.
Instead of saying false statements, we talk around our lies. We circle the truth. We imply things. So you can tell when the US lies by watching for a response that doesn't quite address the question.
Now before you get all x-files, the US government also doesn't like to talk about ridiculous things. So when you read about how the US doesn't talk about aliens, it doesn't mean we are lying about them, it just means we think it's ridiculous. Same thing for Bigfoot, birthers and truthers and vaccine myths as well.
So how do you tell if we are lying or if we think it's ridiculous. Well, there's an easy question you can ask - what do the scientists think - the official experts. If they laugh at the ideas, then it's ridiculous. It doesn't matter what YOU think, you aren't the government. The government is run by people that respect experts. As such, if the experts think it's ridiculous, the the US government thinks it's ridiculous, and won't talk about it.
In addition the US government will definitely make the following lies:
- We will lie about who we are targeting. (Why no sir, we are not investigating that wealthy Pakistani for terrorism charges)
- Who we trust and who we think is lying to us. (Look at the wiki-leaks)
- About where we spent the federal budget.
- Our plans for the future (whether it's future budget, future missions, research for new devices), that have not yet been achieved.
- Taxes. Almost every president ever has had to downplay what they intend to do about taxes - including Reagan. We all want them to lower it, but we want to buy the nice things - like healthcare - that cost us taxes.
- Their own personal political opinions both about issues and about their political competition. I.E. Some republicans that think Obama is a great guy will still insult him for partisan reasons. They need to satisfy their constituents, the party power brokers, and to support their own party. This is less imperative for Democrats, because the DNC is a 'big tent', willing to accept dissent, while the GOP keeps trying to kick the 'Republicans In Name Only" (RINO's) out, eliminating the moderates.
That's what the US lies the most about - we lie about the Future.